Isolation and characterization of phosphate solubilising bacteria from Pb contaminated and Pamended

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Isolation and characterization of phosphate
solubilising bacteria from Pb contaminated and
P-amended soils
Jin-Hee Park, Nanthi Bolan, Ravi
Naidu, Megharaj Mallavarapu, P. Loganathan, and
Kwon-Rae Kim
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Outline
Milestones Lead immobilisation P
solubilisation Objectives Methods used Results
and discussion Conclusions
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Milestones

• Research milestones
• 2.1.1. Laboratory based development and testing
  of the chemical immobilising technology
• 2.1.3. Optimise conditions for
  phytostabilisation and remediation of heavy
  metals
•  
• Commercial milestone
• 2.1.3. Develop and test metal(loid)
  contaminated soil remediation technology

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Lead immobilisation

• Pb is toxic to human, plants, animals and
  microorganisms.
• Pb toxicity can be mitigated by reducing its
  bioavailability.
• The bioavailability of Pb can be reduced by
  immobilizing Pb as phosphate, carbonates and
  hydroxides
• The solubility of Pb-phosphate compound is very
  low log solubility product constants(Log Ksp).
  (Lead phosphate -11.43, Lead hydroxypyromorphite
  -76.8, Lead chloropyromorphite -84.4)
• Phosphate compounds are very effective in the
  precipitation of Pb.

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P solubilisation

• Both soluble and insoluble phosphate compounds
  have been used to immobilize Pb.
• However, the addition of soluble Phosphate
  compounds can result in the leaching of P.
• Insoluble phosphate compounds such as phosphate
  rocks can be used to immobilize Pb these
  compounds can be solubilised using phosphate
  solubilising bacteria (Pseudomonas, Bacillus and
  Rhizobium sp.)
• The activity of phosphate solubilising bacteria
  is affected by enrichment of soil with P and Pb
  compounds.

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Objectives of research

• Overall objectives
• To examine the role of phosphate solubilising
  bacteria in the solubilisation of P in soils
• To evaluate the potential value of rock
  phosphate in the immobilization of Pb through
  lead phosphate precipitation by phosphate
  solubilising bacteria.
• Specific objectives
• To isolate and quantify phosphate solubilising
  bacteria in phosphate emended and Pb contaminated
  soils
• To examine their efficiency in solubilising
  insoluble phosphate compounds.

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Methods used

• Olsen P and Bioavailable Pb extract with
  Ca(NO3)2 of P or Pb enriched soils were
  analysed.
• P or Pb enriched soil samples were used to
  isolate PSB.
• Bacterial population (CFU) was calculated by
  plate counting method.
• PSB were purified and cultured using NBRIP
  medium.
• Solubilised P from the insoluble P Ca3(PO4)2
  by PSB was measured by Murphy Riley method.
• Phosphatise enzyme activity and organic acids
  (lactate, acetate, propionate, pyruvate,
  malonate, maleate, tartarate, oxalate, succinate,
  fumarate, citrate and trans-aconite) were
  measured.

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Soils which were used for PSB isolation
Soils from Kwon-Rae Kim Soils from P.
Loganathan
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Isolating of PSB from soil
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Population of PSB in Pb contaminated soils and
P-amended soils
No. of isolated PSB (CFU/106)
y 0.68x 3.96 R2 0.88
Olsen P (mg/kg)
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Phosphorus solubilisation of PSB
P, organic acid, phosphatise activity
Isolated bacterial strains
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Factors affecting on phosphate solubilisation
Mechanism pH reduction by production of organic
acids (Ca2)m(PO43-)n (HA) (H) (PO4 3- )
(Ca2) (A-) (HA) Microbially produced organic
acids
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Conclusions

• P-amendment could promote the activity of
  phosphate solubilising bacteria while Pb
  contamination reduced their activity.
• Bacterial strains isolated from P-enriched soils
  solubilised more than 350 mg/kg of P from
  insoluble phosphate and these bacteria have great
  potential in the immobilisation of lead in
  contaminated soil.
• Major mechanism of P solubilisation by bacteria
  is considered as the pH reduction through
  production of organic acids by bacteria.

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Acknowledgement

• CRC CARE Scholarship
• CRC CARE Members